TBC1D15 belongs to TBC(Tre-2/Bub2/Cdc16)domain family and functions as GTPase-activating proteins(GAPs)for Rab GTPase.TBC1D15 of Chiloscyllium plagiosum was first found in liver and possessed RabGAP activity on Rab11a and Rab7a.We analyzed shark TBC1D15 gene and predicted the GAP domain at the carboxyl terminal,so we designed several truncations and screened the high-quality protein termed as Shark GAP.Using sitting-drop diffusion and hanging-drop vapor diffusion methods,we got high-resolution crystals which grown at 1.35M Ammonium Sulfate,0.09M BIS-TRIS propane(pH7.0)and 0.01M Calcium chloride dehydrate.X-ray diffraction data of Shark GAP were collected at SSRF(Shanghai Synchrotron Radiation Facility).Crystal structure of Shark GAP was solved by molecular replacement using homologous Sus scrofa TBC1D15 GAP(not published)as an initial model.Comparison of the structures of Shark GAP and Yeast Gyp1p,there are several obvious difference between them.Moreover,key catalytic residues of Arginine and Glutamine in IxxDxxR and YxQ,respectively,also show new orientations to Gyp1p.GAP assays were determined about Shark GAP,the results show that Shark GAP can increase the hydrolysis of Rab7a and Rab11a.But if the conserved catalytic Arg and Glu are mutated to Ala or Lys,the catalytic function of Shark GAP will be lost.Besides,Shark GAP has higher catalytic activity on Rab11a than on Rab7a.In conclusion,we get new structure about shark TBC1D15 GAP domain and determine the function of conserved residues on catalytic reaction.